[unreadable] Over the past decade, investigations using genetically-engineered mice have led to new insights into the genetic control of embryonic vascular development, which has also had a major impact on our understanding of neovascularization in diseases such as cancer and diabetic retinopathy. Noninvasive micro-imaging methods such as ultrasound biomicroscopy (UBM) and high-resolution magnetic resonance imaging (MRI) can play an important role in this research, enabling direct in utero visualization of the developing mouse embryo. We have pioneered the use of UBM and UBM-guided Doppler ultrasound for in vivo anatomical and functional cardiovascular development in normal and mutant mouse embryos. MRI of live embryos has been more difficult, but several groups have shown the utility of contrast-perfusion for high resolution MRI analysis of vascular structures in fixed mouse embryos. Lacking in these studies has been the ability to image molecular targets directly, to better understand and correlate gene expression patterns with morphological and functional data provided by UBM and MRI. Recent advances indicate that cell-specific vascular imaging should be possible using ultrasound and MRI contrast agents targeted to specific endothelial cell receptors. This strategy is likely to be successful first in transgenic mice that over-express defined receptors from endothelial cell-specific promoters, although similar approaches may enable future imaging of endogenous receptors in mice and men. Targeted ultrasound contrast agents have the additional advantage of potentiating in vivo cell-specific gene delivery, via ultrasound-mediated transfection, or sonoporation. [unreadable] The specific aims are: [unreadable] [unreadable] 1) To produce transgenic mice over-expressing Transferrin Receptor (TfR) from endothelial promoters. [unreadable] 2) To determine optimal conditions for sonoporation in the mouse embryonic cardiovascular system. [unreadable] 3) To develop and test TfR-specific contrast agents for in utero targeted UBM imaging and sonoporation of the mouse embryonic cardiovascular system. [unreadable] 4) To develop and test TfR-specific contrast agents for targeted vascular MRI in fixed mouse embryos. [unreadable] [unreadable] The approaches developed in this project will provide powerful new tools for direct analysis of vascular development in living mouse embryos. Significantly, these new molecular imaging methods will provide, for the first time, the ability to detect gene expression in utero in normal and genetically-engineered mice. (End of Abstract) [unreadable] [unreadable] [unreadable]